What order will they speak in?

ITV has produced a table of the speaking order for opening and closing statements, as well as questions. Green Party leader Natalie Bennett will kick things off, while David Cameron has the good fortune of having the last word.

(Source: ITV)

What are the rules?

Each leader will be asked four questions which have been vetted by an ITV panel. This will be followed by an 18-minute discussion on the topic raised by the question.

What's the format?

The leaders will answer questions in front a 200-strong audience which has been carefully selected to reflect the UK's ethnic, age, gender and social make-up. The questions have been selected from the submissions of viewers and audience members. The debate will be two hours in total.

Who's tipped to win?

Anything could happen tonight, and everyone will have their own hunches about who will come out on top but the bookies have Ukip leader Nigel Farage as their favourite to win.

When will we know who's won?

At 10:00pm ComRes will release a snap poll of who viewers think won the debate. This will only be a snapshot - the view could change over time, but it will be the first indicator of who had a good night and who failed to impress. There will also be a YouGov poll that will be released after the ComRes poll.